Siliconized silicon carbide connection and method of making the same



M 1943 H. HEYROTH 2,319,323

SILICQNIZED SILICON CARBIDE CONNECTIONS AND METHOD OF MAKING THE SAME Filed June 8, 191,8

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INVENTOK A/berf He ro/h ATTORNEY Patented May 18, 1943 SILICONIZED SILICON CARBIDE CONNEC- l'ION AND METHOD OF MAKING THE SAME 'Albert II. Heyroth, Niagara Falls, N. Y., asslgnor to The Carborundum Company, Niagara Falls, N. Y., a corporation of Delaware Application June 8, 1938, Serial No. 212,540 In Great Britain April 11, 1938 10 Claims.

This invention relates to silicon carbide articles particularly those suitable for use as electrical resistors, and to a. method of making the same.

Silicon carbide resistors, particularly those made by recrystallizing the silicon carbide, have been found to be highly useful, but their use has been limited by the fact that they could be made only in simple shapes, for example in straight rod-like shapes, and by the difliculty in providing such resistors with suitable cold ends at low cost.

The "cold ends referred to are the ends of the rod that engage the holding means by which the resistors are supported and by which the electrical energy is supplied to the rod. They ,are called cold ends because they have been made to have a lower specific resistance than that oi the rod proper in order that they might not get as hot as the main body of the resistor. A lower temperature at the ends of the rod has been found to be highly desirable because otherwise the contact between the rod and the supporting member itself, for that matter, would soon destroyed by the high temperature at= tained in the main body of the rod.

@ne object of the present invention is to pro= vide silicon carbide resistors not restricted to the simple shapes heretofore made and to pro= vide suitable terminal portions, or cold ends) at a reasonable cost. Other objects oi. the in ventioo. will become apparent from the following disclosure.

a better understanding the invention may be had by referring to the appended drawing.

Fig. l is a plan view of one type of resistor;

Fig. 2 is a side plan view partly in section, oi another embodiment;

Fig. 3 is a plan view of another embodiment; and

Fig. i is a view of still another embodiment.

Figure 1 represents an embodiment of the present invention comprising a resistor oi hex agonal shape made by integrally uniting a plu= rality of straight, rod-like resistors l0, and terminal members It by means of welds l2.

Silicon carbide rods made by recrystallizing the compact variety of silicon carbide, or mire tures of the compact and regular varieties by passing a current of electricity through the rod are one tom of resistor that can be used. to advantage in the construction of an article such is iiiustrated in Figure 1 members it of the article illustrated in Figure i can made by subjecting rods of recrystallized silicon carbide, as referred to above, or of porous carbon, such as charcoal, bonded by a carbonizable material, such as casein, to a siliconizing treatment at the temperature at which molten silicon rapidly penetrates such bodies. This temperature is believed to be above approximately 1800 C. Such rods will be referred to hereafter as being of siliconized silicon carbide, such reference being proper because silicon carbide is formed in the porous carbon body by the silicon treatment and, naturally, there is silicon carbide in the body made by siliconizing the recrystallized silicon carbide body referred to above.

The article illustrated in Figure l is made by welding the component parts into an integral structure through the use of silicon. The ends to be joined are coated with a paste comprising carbon, a carbonizable binder, such as casein, and water and are then brought together on a plate of carbon, which can be heated to a high temperature by virtue of its being part of an electrical circuit. A small quantity of granular silicon is placed at the joint in contact with the parts to be joined current is then passed through the carbon plate to raise its temperature rapidly. The parts being joined and the granular silicon likewise are raised in temperature, until the silicon permeates the porous carbon rod to form substantial amounts of silicon carbide crystals within the rods. The cementing substance used at the joints is likewise acted upon by the silicon to form a weld uniting the individual parts into an integral object.

A splicing or welding composition which 1 have found highly suitable for cementing the joints between the separate parts of the resistors is made up of the following ingredients:

Grams Flour 200 Carbon 500 Charcoal 200 ture control device.

readily be adapted as an element for a tempera- In Figure 2, a helical element i3, the central terminal rod l4 and the outer sleeve or terminal ii are made up separately from a mix of porous carbon and casein glue similar to that used in making'terminal elements ll of Figure 1. These parts are then joined together at points l6 by means of a welding mixture and subjected to a temperature of at least 1800 C. in the presence of granular silicon, whereupon the individual parts are permeated by siliconand transformed into a siliconized silicon carbide body. At the same time the joint become welded to form an integral article. The terminal rod I4 and terminal sleeve I are maintained in spaced relationship by means of an insulating refractory cement il.. If desired, the individual parts may be treated with silicon first to form the separate silicon carbide bodies and later welded together in the manner described.

Figure 3 illustrates a silicon carbide resistor element of conventional rod shape which has been cold-ended in accordance with the invention.

In Figure 3, the main body portion of the rod l8 ismade of recrystallized silicon carbide formed by passing a. current of electricity through a rod formed from the regular or compact variety of silicon carbide. To each end of this rod silicon carbide end pieces It made from the carbonaceous mix referred to above in Figure 2 are cemented by means of welding composition such as that referred to above to form joints 20. The end pieces l9 and joints 20 are then subjected to a temperature above. approximately 1800 C. in

' the presence of granular silicon which when heatsilicon carbide and/or parts of siliconized silicon carbide made from a mixture of porous car-' bon and carbonizable materials. The latter type of body can be treated prior to the welding operation to form a body containing silicon carbide such resistor bodies. Most important of properties in this respect is its extremely low specific resistance (as compared to recrystallized silicon carbide bodies), whereby in operation considerably less watts are generated and the resulting temperature of the cold-end considerabb' lowered. Such material also has a much lower electrical contact resistance whichtends to prevent it from arcing at the points of contact with the terminals or terminal rods and therefore cuts down on localized heating or hot spots. When such arcs do occur through a faulty mechanical contact there is less tendency to sustain the arc than in the former type ofcold-ended resistor.

It is possible also by the present method of cold-ending resistors to cut down on heat losses through overheating of the terminal portions of resistor elements and also to eliminate costly water-cooling units used with the former type of resistor set-ups.

These and other advantages which readily become apparent are obtained by the use of resised permeates the and rods and joints to integrally unite them to the main rod giving a coldended resistance element.

\ Figure 4 illustrates a helical heating element having a main body portion 2! and the two straight and or contact portions 22 joined by welds at the points 22; The parts 2i and 22 are siliconized silicon carbide bodies formed from pcrous carbon bodies which have been siliconized by subjecting them in the presence of silicon to a temperature in'excess of approximately 1800" C. The helical part 2| is formed by extrusion. The separate parts 2i and 22 are cemented together at the points 23, before or after siliconizing, by means of a welding composition such as that previously given and subjected to a ternperature above approximately 1800 C. in the presence of silicon. When the assembly and the silicon are heated to such a' temperature the silicon permeates the joints and parts to integrally unite into an integral resistance element. At,

such temperatures and even at much lower temperatures silicon shows afinity for carbon as indicated by the formation of silicon carbide from silicon and lampblack at temperatures as low as 120W 0. Silicon carbide with an excess of liquid silicon forms on solidification of the silicon a strong joint of comparatively high electrical con ductivity and high thermal conductivity.

In addition to the specific examples already given, many other shaped articles can m made by welding together parts made oi recrystallized tor elements cold-ended by welding terminal portions of siliconized silicon carbide to a recrystallized central heating portion by means of a weldingcompound and treatment herein presented.

Having described my invention, what I claim is 1. A compound resistor comprising a plurality of bodies of predetermined size and contour composed principally of recrystallized silicon carbide and integrally united by means of welds containing silicon admixed with silicon carbide.

2. In the manufacture of silicon carbide alrticlescomprising a plurality of individually preformed silicon carbide shapes of predetermined size and contour, the process of welding a joint between two of the siilcon carbide shapes which comprises coating the joint with a carbonaceous composition and raising the temperature of the joint in the presence of silicon to such a degree and for such a time that the said silicon permeates the joint and the silicon carbide shapes adjacent the joint, and that anintegral article is formed on the solidification of the silicon.

3. In the manufacture of silicon carbide articles comprising a plurality of individually pre-.

carbonaceous mix, and raising the temperature of the joint in the presence of silicon to such a v degree and for such a time that the said'silicon permeates the joint and the silicon carbide shapes adjacent the joint, and that an integral article is formed on the solidification of the silicon.

4. In the manufacture of silicon carbide resistance elements, the steps which comprise formshapes consisting essentially of silicon carbide, and other of said shapes consisting essentially of porous carbon and a carbonizable substance, placing a silicon carbide shape in approximate contact with a shape of porous carbon and carbonizable substance, joining the two shapes by means or a carbonaceous mix, raisng the temperature of the joint in the presence or silicon until the silicon penetrates the joint to integrally unite the two shapes and also heating the porous carbon shape in the presence of silicon to convert it to siliconized silicon carbide.

5. A cold-ended silicon carbide resistor comprising a main resistor of recrystallized silicon carbide, terminal bodies of siliconized silicon carbide having outwardly extending portions of reduced cross-section and joints of siliconized silicon caribde connecting said main resistor with said terminal bodies in which joints silicon carbide is formed in situ by impregnating a carbonaceous cementing mixture with silicon at tempeatures which cause a strong absorption of elemental silicon into the joint and the adjacent bodies.

6. In the manufacture of silicon carbide reand contour of siliconized silicon carbide, the

steps which comprise placing one 01' the said shapes of silicon carbide in approximate contact with one of the said shapes of siliconized silicon carbide, joining the two shapes by means of a carbonaceous mix, and raising the temperature r of the joint just formed in the presence of silicon to such a degree and for such a time that the said silicon permeates the joint and the silicon carbide shapes adjacent the joint, and that an integral article is formed on the solidification of the silicon. Y

7. In the maniacture of silicon carbide resistance elements comprising at least one individually preformed recrystallized silicon carbide shape predetermine size and contour and at least one individually preformed siliconized silicon carbide shape of predetermined size and contour, the steps which comprise placing one of the said shapes of recrystallized silicon carbide in approximate contact with one of the said shapes 0! siliconized silicon carbide, joining the two shapes by means of a carbonaceous mix. and raising the temperature of the joint just formed in the presence of silicon to such a degree and for such a time that the said silicon permeates the joint and the silicon carbide shapes adjacent the joint, and that an integral article is formed on the solidification oi the silicon.

body with both in the presence of silicon to such a degree and for such a time that the said silicon permeates the Joint and the porous carbon body adjacent the joint, and that an integral article is formed on the solidification oi. the silicon, and until the porous carbon body is converted to a siliconized silicon carbide body.

9. In the manufacture of a compound resistor comprising a plurality of individually preformed z shapes composed principally of recrystallized silicon carbide, said shapes being of predetermined size and contour, the steps which comprise placing two of the said shapes in approximate contact with one another, joining the two shapes by means of a carbonaceous mix, and raising the temperature of the joint just formed in the presence of silicon to such a degree and for such a time that the said silicon permeates the joint and the silicon carbide shapes adjacent the joint, and that an integral article is formed on the solidification of the silicon.

10. A cold-ended silicon carbide resistor comprising a main resistor 01 recrystallized silicon carbide, terminal bodies of siliconized silicon carbide, and welded joints of siliconized silicon carbide connecting said main resistor with said terminal bodies in which welded joints silicon carbide is formed in situ by impregnating a carbonaceous cementing mixture wtih silicon at temperatures which cause a strong absorption of elemtal silicon into the joint and the adjacent ALBERT H. HEYROTH. 

